1. Field of Invention
The present invention relates to energy conservation in industrial plants and other facilities. More particularly, the present invention relates to control of reactive power consumption in such plants and facilities.
2. Description of the Prior Art
It has become a common practice in industrial facilities to pay increased attention to energy conservation programs. Efficient usage of electrical energy has become a matter of increasing concern, and electrical energy costs often are an important factor in overall expenses of an industrial plant or other facility driven by electrical power.
Where electrical power is furnished as alternating current (or AC) power, one way to save energy has been to improve the power factor (PF). As is known, the power factor of alternating current in a system is the ratio of real power to apparent power, or in effect the cosine of the phase angle between voltage and current in the system. Conventional methods of power factor (or PF) improvement have used two techniques. One type has capacitor banks, while the other has used compensators known in the art as VAR compensators. However, so far as is known, traditional methods of power factor improvement have not supervised or monitored the overall power system at the plant or facility of interest. There has been, so far as is known, no dynamic control or feedback obtained based on system operating parameters as an attempt to optimize power factor correction or improvement.
Certain industrial facilities have often employed considerable synchronous motor loads. For example, a typical natural gas processing plant may have from 40% to 45% of the electrical load composed of synchronous motors which drive large gas compressors. It has also been recognized that synchronous machines have the ability to generate reactive power. However, these motors have operated in industrial plants at a constant power factor, without considering either overall system performance or dynamic changes in the plant's power distribution system during operation. As a result, considerable amounts of electrical power beyond that actually needed for the actual plant electrical load have been required to be imported to meet actual load requirements. The imported power was costly, and often was at even higher or premium rates when imported at times of peak demand.